“I feel forest breathing / and hear the inexorable growth of the wood,” the sculptor Giuseppe Penone wrote in 1968, “I match my breathing to that of the green world around me.” Penone, who is now 74, has long been mesmerized by nature, especially trees, which he sees as sculpture. He describes a tree’s growth as a creative process “made up of fingerprints, finger marks, traces of oil … felt, followed, touched, point by point.” In “Alberi In-Versi,” 30 works in various mediums invoke trees. Penone sculptures are also on display throughout the city, including the colossal Abete, a spidery 22-meter-high tree installation on view in Piazza della Signoria. —E.C.